The present invention relates to a vehicle headlamp leveling device for estimating a pitch angles of a vehicle in its longitudinal direction and automatically tilting the axes of headlamps to cancel the pitch angle.
In a headlamp, a reflector, in which a light source is securely inserted, is tilted around a horizontal tilting shaft relative to the body of the headlamp. The optical light axis of the reflector (or the headlamp) is arranged to be tilted by an actuator around the horizontal tilting shaft.
When luggage is loaded in or unloaded from the vehicle or occupants in the vehicle get in or out while the vehicle is at a stop or stationary, the load acting on the vehicle changes and the pitch angle of the vehicle may change. However, in most cases, both the front and the rear of the vehicle sinks or is lowered. When a vehicle height at the rear (a distance between the axle and the body) detected with a vehicle height sensor provided on a rear suspension and a pitch angle are correlated, an approximate line can be estimated, with the assumption that the front of the vehicle is lowered. Then, a pitch angle can be calculated based on an output from the vehicle sensor and the estimated approximate line.
A conventional vehicle headlamp leveling device comprises a vehicle height sensor provided on either the left or right suspension of either the front or rear of the vehicle for detecting a distance between the axle and the body, a storage part in which a correlation function (an approximate line) between outputs from the vehicle height sensor and pitch angles of the vehicle is entered and set as control data, and an operation control part for controlling the driving of actuators based on an output from the vehicle height sensor. The control data (the approximate line) is stored in the storage part such that a predetermined inclined state of the optical light axes of the headlamps is maintained relative to a road surface.
When a load on the vehicle changes, the vehicle height sensor detects the change and outputs the change to the operation control part. The operation control part then calculates a vehicle pitch angle corresponding to the output from the vehicle height sensor based on the correlation function (the approximate line which is entered and set in advance) between outputs from the vehicle height sensor and pitch angles of the vehicle. The control part then drives the actuators (tilts the optical light axes of the headlamps) only to an extent corresponding to the calculated pitch angle.
The correlation function between outputs from the vehicle height sensor and pitch angles of the vehicle, which is stored in the storage part in advance, is specified by a single approximate line with the assumption that the vehicle is lowered also at the front. However, if luggage is put into a protruding section of the vehicle such as a trunk, the front of the vehicles rises (or lowers less) compare to the rear, and the actual pitch angle deviates far from the approximate line. Hence, an appropriate pitch angle of the vehicle cannot be obtained, and the headlamps cannot be appropriately leveled.
FIG. 2 is a chart showing a correlation between outputs from the vehicle height sensor (abscissa) and pitch angles of the vehicle (ordinate). D denotes that the driver is seated in the driver""s seat, P denotes that the front passenger is seated in the front passenger seat, R denotes that a rear seat passenger is seated in the rear seat, and L denotes that luggage is loaded in the loading space such as a trunk (for example, a load of 100 kg). For example, DPR shows data taken when the driver, front sea passenger and rear seat passenger are seated in their respective seats. DPRRL shows data taken when the driver, front seat passenger and two rear seat passengers are seated in the respective seats with luggage loaded in the loading space to its given or maximum loading capacity. Furthermore, full loading (DPRRRL) shows data taken when the driver, front seat passenger and three rear seat passengers are seated in the respective seats with luggage loaded in the luggage space to its maximum loading capacity. Full loading (D) shows data taken when only the driver is seated in the driver""s seat with luggage loaded to the maximum loading capacity.
In the conventional automatic headlamps leveling device, the correlation between outputs from the vehicle height sensor and pitch angles of the vehicle is specified by an approximate line (linear) designated by reference character A for use as control data, with the assumption that the front of the vehicle is lowered.
Although the correlation between outputs from the vehicle height sensor and pitch angles of the vehicle shows a characteristic of increasing linearly as shown in FIG. 2, there is variation of data in the direction of the ordinate axis. If the output from the vehicle height sensor shows xe2x88x922 mm, the operation control part calculates an angle of 0.45 degree as the posture (the pitch angle) of the vehicle. This angle corresponds to an output of the vehicle sensor (xe2x88x922 mm) derived from the approximate linear line designated by A. However, in actuality the vehicle posture (the pitch angle) of the vehicle should be about 0.6 degree (position DL in FIG. 2) but the operation control part controls the driving of the actuators to an extent that corresponds to the value of 0.45 degree and not 0.6 degree, as it should be.
An object of the invention is to provide a vehicle headlamp leveling device for enabling the compensation of optical light axes of headlamps of a vehicle with high accuracy by specifying two or more control lines (approximate lines stored in a storage part) with different slopes that correlates outputs from a vehicle height sensor and pitch angles of the vehicle. An optimum control line (approximate line) from the two or more control lines is selected based on a change in an absolute pitch angle obtained from an output of an auxiliary sensor. The auxiliary sensor detects the absolute pitch angle of the vehicle relative to a horizontal plane.
A vehicle headlamp leveling device according to a first embodiment of the invention comprises headlamps adapted to be driven by actuators such that light axes thereof are tilted up and/or down relative to the body of a vehicle, a vehicle speed sensor provided on the body, a vehicle height sensor provided either on a left or right suspension of either the front or rear of the vehicle for detecting a distance between an axle and the body, a storage part in which control data is entered and set in advance which comprises a correlation function between outputs from the vehicle height sensor and relative pitch angles of the vehicle relative to a road surface, and an operation control part for determining from an output from the vehicle sensor whether the vehicle is at a stop or moving and controlling the driving of the actuators based on an output from the vehicle speed sensor. The control data can be stored in the storage part. With the above embodiment, the optical light axes of the headlamps can stay in a predetermined inclined state relative to the surfaces of roads at all times. The control data in the storage part can be specified by at least two or more control lines that are inclined differently. An auxiliary sensor can be provided on the body for detecting an absolute pitch angle of the vehicle relative to a horizontal plane. The operation control part compares a difference between a variation added pitch angle, which is obtained by adding a variation in the absolute pitch angle to a relative pitch angle calculated from control lines previously selected, and a relative pitch angle calculated from respective control lines based on a current output of the vehicle height sensor. The control part then selects a control line with the smallest difference and controls the driving of the actuators based on a relative pitch angle calculated from the selected control line.
If the relative pitch angle calculated from the previously selected control line (the pitch angle of the vehicle determined previously) is assumed to be an accurate value, the variation added pitch angle, derived by adding the variation in the absolute pitch angle to the relative pitch angle, is also an accurate value. Consequently, among the relative pitch angles calculated from the respective control lines (approximate lines), a relative pitch angle closest to the variation added pitch angle approximates an actual pitch angle (an inclination) of the vehicle.
For example, as shown in FIG. 2, assume that the previously selected control line is B and that the output from the auxiliary sensor is xcex94xcex8. The variation added pitch angle (xcex8B+xcex94xcex8), obtained by adding xcex94xcex8 and the pitch angle xcex8B calculated from the control line B (the previous pitch angle of the vehicle), is compared with pitch angles xcex8b, xcex8c calculated from the control lines B, C, respectively, based on a current output of the vehicle height sensor. Whichever of the two pitch angles xcex8b, xcex8c, closer to the variation added pitch angle (xcex8B+xcex94xcex8) is also closer to the actual incline of the vehicle.
That is, differences between the variation added pitch angle (xcex8B+xcex94xcex8) and the pitch angles xcex8b, xcex8c calculated from control lines B, C based on the output from the vehicle sensor this time are obtained, respectively. The control line B (or C) of the control lines that shows a smaller difference is selected as a control line more appropriate for determining the current correlation. The driving of the actuators is controlled based on the relative pitch angle calculated using this selected control line B (or C).
According to a second embodiment of the invention, a vehicle headlamp leveling device has a vehicle height sensor provided on one of the rear suspensions, and a control data comprises two control lines representing two cases where a load is placed in a rear overhang portion such as a trunk and where no load is placed, respectively.
Assume luggage is placed in the overhang portion such as the trunk with the vehicle height sensor provided on the rear suspension. Since the front of the vehicle is lowered less compared to when no load is placed, the correlation between outputs from the vehicle height sensor and pitch angles of the vehicle can be specified by two correlation functions represented by a control line (an approximate line) corresponding to luggage placed in the rear and a control line (an approximate line) corresponding to no luggage.
In addition, the first and second embodiment are premised on the leveling (the compensation of the optical light axes) of the headlamps based on pitch angle data taken from a vehicle at a stop. The pitch angle data of a stationary vehicle would be more accurate than those of a moving vehicle to an extent that there are fewer factors that perturb a stationary vehicle. Thus, since the actuators are controlled based on the more accurate pitch angle data, the automatic headlamps leveling can also be accurate to that extent.
According to a third embodiment of the invention, a vehicle headlamp leveling device has an operation control part adapted to control the actuators when the vehicle is moving stably. The control is based on a relative pitch angle calculated from a last selected control line of the vehicle at a stop. A vehicle is defined as moving stably if it runs at a speed that is equal to or greater than a given value and runs with an acceleration that is equal to or smaller than a given value.
If the automatic leveling of headlamps is limited only to stationary vehicles, inappropriate pitch angle data collected, for example, while the vehicle is parked on a slope or with a wheel or wheels riding on a curb, may be used to level the headlamps (compensate the optical light axes). An inappropriate leveling of the headlamps can be avoided by controlling the actuators based on pitch angle data detected when the vehicle is running stably, a condition that approximates the vehicle at a stop.
According to a fourth embodiment of the invention, a vehicle headlamp leveling device has an operation control part and a storage part constructed as part of an ECU. The ECU comprises CPU, RAM and ROM, and an auxiliary sensor.
The incorporation of the auxiliary sensor into the ECU reduces the number of constituent components of the automatic headlamps leveling device.